1. Field of the Invention
The present invention relates to a releasable self-adhesive film laminate for a label or card, as well as a label or card having such a releasable self-adhesive film laminate. Specifically, the present invention concerns a label or card in which the printed surface of a label substrate, etc., is usually concealed by a film laminate but it can be revealed as required.
Such a type of label or card is already known, as disclosed in, for example, Japanese Utility Model Publication No. Sho 55-36858 under the title of "Sealed Sticker". In this sticker, a transparent film is attached to a printed surface of a label paper by means of a strong pressure-sensitive adhesive layer, and a top label, i.e., a cover seal is bonded releasably to the upper surface of the transparent film by means of a weak adhesive layer.
If a user wishes to remove the cover seal, the cover seal can be peeled off the upper surface of the film, leaving the film on the label paper, owing to the difference in bonding strength between the strong and weak adhesive layers. The user can then enjoy the print revealed on the first label paper, through the transparent film.
Recently, demands have increased for practical sealed labels or cards, such as a lottery ticket with a prize number that is usually concealed, or a sealed postcard used as a substitute for a letter sealed in an envelope. Although various ideas for such goods have been proposed, most of them utilize pressure-sensitive adhesives as described above and, accordingly, involve the inconvenience that the stickiness of the adhesive remains to some extent after the seal cover is peeld off.
In addition, control of the difference in bonding strength between the adhesive layers on either side of the film is not easy. If the adhesion of the cover seal were too great, the film would be peeled off the label paper together with the cover seal, damaging the surface of the label paper. On the other hand, if the adhesion of the cover seal were insufficient, the cover seal could peel off easily during usual handling.
In view of the above, the present inventor, et al., proposed a postcard having a releasable bond surface between adjacent film layers in, for example, U.S. Pat. No. 4,742,954 (Japanese Utility Model Laid-Open Sho 63-6870). In our proposed postcard, a cover sheet (seal) is releasably attached to the surface of a card substrate by laminated film layers.
In this postcard, the laminated film layers comprise, as stated in the claim, a transparent protection film 2 made of a thermoplastic resin bonded by means of an adhesive layer 7 to the upper surface of a card substrate 1, a film 3 which is made of a thermoplastic resin different from that of the film 2 and which is firmly laminated onto the under surface of a cover sheet 4, and a coupling film layer 5 made of the same thermoplastic resin as that of the film 3. The film 5 is inserted in a melted state between the cover sheet 4 and the film 2, and is bonded firmly to the film 3 under the cover sheet 1 while being bonded releasably to the upper surface of the film 2.
The adhesion formed between the adjacent films 2 and 4 is unique in that its peeling strength can be freely varied by controlling the melting temperature of the film 5 and by selecting a suitable combination of materials for the two film layers 2 and 5, and in that none of the surfaces of the films 2 and 4 exhibits any stickiness after being peeled away from each other.
Such distinctive adhesion formed between different kinds of thermoplastic film layers is referred to as "pseudo adhesion", and it is currently utilized in practice to answer many requirements. We have also proposed several applications for this form of adhesion in, for example, Japanese Utility Model Laid-Open Nos. Sho 63-21068 and 63-21069.
The features of "pseudo adhesion" are practical and convenient. However, it still involves problems. The first problem is that the manufacture of the three-layer film structure with a "pseudo adhesion" boundary is troublesome and also expensive. Next, as is well-known, temperature control is one of the most delicate factors of plastic molding. Accordingly, accurate adjustment of the pseudo adhesion strength requires considerable skill. In addition, the optimal melting temperature for the target bonding strength varies with every combination of resin materials.
In view of the above, it is a first object of the present invention to provide a releasable self-adhesive film laminate comprising a pair of films, made of the same kind of thermoplastic resin and releasably joined to each other, that can be used as an element for a label or card equipped with a releasable seal.
It is a second object of the present invention to provide a label equipped with a releasable seal that can be manufactured easily and at a low cost.
It is a third object of the present invention to provide a card equipped with a releasable seal that can be manufactured easily at a low cost and also be convenient to use.
The first object of the present invention can be attained by a releasable self-adhesive film laminate designed for a sealed label or card having a pair of transparent films prepared by blow-molding a thermoplastic EVA composition comprising about 3 to 18% by weight of vinyl acetate and about 97 to 82% by weight of ethylene at a molding die temperature of about 120.degree. to 210.degree. C. to form a hollow tubular film body, and then urging facing wall surfaces of the molded tubular body, while hot, under pressure to laminate and releasably bond them to each other.
The second object of the present invention can be attained by a label equipped with a releasable seal, the label having:
a label substrate of which one surface is to have a printed or written massage,
a cover seal attached releasably over the printed or written surface of the label substrate, and
a releasable self-adhesive film laminate firmly sandwiched by means of transparent pressure-sensitive adhesive layers between the label substrate and the cover seal, to releasably bond the cover seal to the surface of the label substrate, wherein
the releasable self-adhesive film laminate comprises a pair of transparent films, each made of a thermoplastic EVA composition comprising about 3 to 18% by weight of vinyl acetate and about 97 to 82% by weight of ethylene prepared by a thermoforming process and by being bonded to each other while hot under pressure.
The third object of the present invention can be attained by a card equipped with a releasable seal having:
a card substrate with one surface having a printed or written message which is intended to be concealed,
a cover seal of a high hiding power attached releasably over the card substrate, and
a releasable self-adhesive film laminate sandwiched by means of transparent pressure-sensitive adhesive layers between the card substrate and the cover seal, wherein
the releasable self-adhesive film laminate comprises a pair of transparent films, each made of a thermoplastic EVA composition comprising about 3 to 18% by weight of vinyl acetate and about 97 to 82% by weight of ethylene prepared by a thermoforming process and by being bonded to each other, while hot, under pressure thereby forming a releasable boundary between the paired films.
The releasable boundary between the paired layers of the film laminates are slit at least one peripheral portion thereof and heat-sealing is further applied to the outer edge of the peripheral edge that was slit.